Film motion filter



April "5; 1938. H. J. HASBROUCK. JR 2,112,894

FILM MOTION FILTER Filed March 28, 1936 INVENTOR Harald LT. Hashrnunk.LII.

BY W/FMW ATTORNEY Patented Apr. 5, 1938 FILM MOTION FILTER Harold J.Hasbrouck, 11-, Merchantville, N. 1.,- signor to United ResearchCorporation,-Burbank, Calif., a corporation of Delaware ApplicationMarch 28, 1936, Serial No. 71,532

13 Claim.

This invention relates to talking motion picture apparatus andparticularly to the film drive portion of the sound recording orreproducing unit wherein the motion-of the film past the translationpoint is maintained constant. It is well understood that a necessaryprerequisite for perfect sound recording and reproduction is that thefilm be advanced at a constant and uniform speed through the light beam,the point of contact between the film and beam being known as thetranslation point. Stabilizing devices such as flywheels have been andare employed for stabilizing the motion at this point against theeffects of starting surges, take-up reel jerks, me-

chanical faults of the driving mechanism, or other extraneous causes ofspeed variations. The flywlieels may be supplemented byother mechanicalfilter elements having, for example, elastic and/or resistivecharacteristics toaid instabilization.

In the types of filter elements having mechanical resistance areincluded dash pots employing viscous mediums such as oil. Such an oildash pot has heretofore been used to control the movement of a resilientrestoring element acting on a loop in the film between the drivesprocket and the flywheel roller which guides the film at thetranslation point.

The present invention is directed to an improvement in -a filter of thistype, this improvement consisting of a particular form of slidingfriction as the damping element instead of a viscous friction such asproduced by oil in the dash pottype of'damping element. Many advantagesof the sliding friction damper, if designed in accordance with thisinvention, are found over the viscous damper, some of which are, freedomfrom attention, independence of temperature changes, no oil leakage.problem and less counterforce during rapid displacements, therebypermitting an adjustment which results in a more rapid decayof filteroscillations initie-ted, for example, by the starting surge.

In the normal sound unit, some of the causes of speed variations notminimized by the flywheel and oil dash pot may be traced to the startingsurge, film reel take-up Jerks, and the variations in friction ofbearings due to poormaintenance. These causes of speed variationsproduce different rates or velocities of filmspeed changes which liewithin determinable frequenoy limits. It has been found in the use of anoil dash pot damper in a filter having a lowperiod that, if the damperisadjusted to provide the proper damping to quickly dissipate the (o1.z'u-aa) Y oscillations initiated by the starting surge, which generallyproduces a low velocity variation, it will ofler such a largecounterforce during any later rapid displacements or variations that theangular "velocityof the flywheel may be substan- 5 tlally altered or thefilm caused to slip on-its roller or drum. Also if it were adjustedproperly for the rapid variations, it would be insumcient to dampen outthe slower variations.

To avoid flywheel speed variations therefore, the damper should notoffer a counterforce so large as to prevent the moving elements of thefilter from promptly accommodating the changed length of loop betweenthe drive sprocket and the drum of .the flywheel caused by rapidvariations nor, should it be so small as to permit the moving elementsto oscillate for an appreciable time. 1 If a viscous type of damper isadjusted to provide sufllcient damping of the fundamental period of thefilter to quickly dissipate the oscillations caused by'the startingsurge, then sudden film speed changes produce sumcient coun-l teri'orceto permit a sudden transfer of energy to the flywheel and consequentlyappreciably alter the speed of the film at the translation point. Thisis becausewith viscous dampers the counterforce increases directly withvelocity, particularly within the velocity limits required by film drivefilters, while 1 for :further increased velocities ac'ounterforceproportional to higher powers ,ofthe velocity may. beproduced caused bythe onset of turbulence in the fluid.

It has also been found that-the ordinary or" usual typeof slidingfrictionhas a static friction greater than its initial kinetic frictionwith the result that the force required to start it in motion isconsiderably greater than the force required to maintain movementthereafter, the trcnsitionoccurring quite rapidly. Such types of slidingfriction are not suitable for the invention since damping would only beaccomplished after a surge of suillcient force was in-- troduced toovercome the staticfriction counterforce. There would thus be set up a.series of transient surges or. parasitic oscillations caused by suchforceacting on the film elastance, and flywheel mass. It has beendiscovered therefore-that the static friction should be substantially'zero or negligible compared'with the operating kinetic friction.

As stated above, if the viscous damper produced sufficient damping atthe low velocities, it would produce entirely too, great a counterforceat the higher velocities, and if it had the Y proper damping efiectatthe higher-velocities,

locity above the critical range of film variation velocities and whichhas a static friction of substantially zero.

For instance. to illustrate with a particular case. a starting surge mayresult in a shortening of the film loop, due to the film being taken outof the loop faster than it is fed thereto by the flywheel roller duringits acceleration up to normal film speed. 'Ihe result is the storing ofenergy in the tensioning means beyond that required for normal film Thisenergy is released when the drum has reached normal speed and, without adamper, this energy release will maintain excess tension in'the mm andcontinue to accelerate thefiywheel. The result of this acceleration is atransfer of energy from the spring to the flywheel which increases theloop beyond its normal size as more film is fed into it by the drumthan: istaken out by :the drive sprocket. a f

'Ihis inter-transfer of energybetween the tensioning means and flywheelproduces oscillations or variations in film speed which are deleteriousto good sound recording or reproduction. Thus, to prevent theseoscillations,the energy should preferably be absorbed by the damperasfast as it isreleased; This is accomplishedby placing a drag on thetensioning means'which will absorb its stored energy. 4

The damper mumalso absorb the energy arising from surges enteringthesystem when normally operating. We can assume for illustration,surges of a higher velocity than that encountered in starting. Now since.the counterforce of the damper of this invention increases less rapidlythan the velocity. we minimise the transfer of energy to the flywheel,store it in the tensionlng means, and dissipate. it at the low freeperiod velocities of-the V An obiect oftheinvention therefore is toobtain a substantially. comtant counterforce to film speed changes oversdcfiniterange, of speedvalocitybelow this range.

This object is accomplished by providing a sliding friction in: a filmloop between the riations andacounterforce proportional to vedrivesprocket and flywheel roller, which damper I has negligiblestaticfriction, a counterforce proportional to velocity for a predeterminedlow range of velocities .and substantialiyvconstant counterforce, for apredetermined higher range of velocities. v 1

One set of materials providing the proper sliding frictioncharacteristicvwas found to be soft 1 felt against stainless steelpolished'to a very high degree. Adeviceemploying these materials-andconstructed to operate with a roller positioned in a loop in the-filmbetweenthe drive sprocket and-fiywheel'roller of a sound recording orreproducing machine was found to. provide a much superior damper for afilm motion filter than the viscous type previously known in the art. Itwas found that by adjusting the pressure between thefelt and the steel,the proper damping could be obtained to dissipate the starting surgebefore completing the first oscillation of the mechanical filter andhence in a muchshorter time than possible with the oil type damper.

With the oil damper, provision against oil leakage and change inviscosity with temperature had to be provided. The present inventionavoids these provisions, is rugged in construction, and may beconveniently adjusted'by a screw for controlling the pressure betweenthe felt and the steel to change the damping. A coil spring maintainsthe pressure between the felt and steel substantially uniform.

The details of the invention will be more fully Fig. 6 is a graphshowing the relationship between the counterforce of friction andvelocity for different dampers. Referring now to'the figures, in whichthe same numeral indicates identical elements, the

soundreproducer of Fig. i is 'includedin ahousing tdivided into twosections 6 and 1. Section 8 enclosesa lamp ll of constant intensity, thelight rays therefrom being projected through a lens and silt assemblytube ll into compartment 1. In compartment I afilm i3 is continuouslyadvanced through the lightbeam from tube ll,

the. driving force being applied by asprocket it having a pad roller llassociated therewith. The film is pulled by the right hand side ofthesprocket, under a roller ll, over a roller I, under a tension roller 20,over a roller II; around the flywheel roller or spool 22 having a guideor pressure roller 23 associated therewith-around a roller 24 and thenfrom the left hand-side of sprocket M which feeds the film II to form a.

slight upper loop between rollers 23 and 24. The roller or spool 22 ismounted on the same shaft with'the fiywheei shown by the dotted lines21.

An optical system It and photo-sensitive device ll projects the emergentlight from the sound track portion of the film i3 and translates it intoelectrical currents, respectively, as is well known in the art. Theparticular system shown at 2! and ll in combination with thespool I2, isdisclosed and claimed in my co-pending application Serial No. 54,885filed December 17, 1935.

The present invention utilizes the damper shown as a unit at 32 andhaving an arm 33 extending therefrom to the roller 20. A tension springis attached to arm I! and to lever 30 pivoted at 42 and having a notchand screw adjustment arrangement 81, provides the means of varying thetension on the arm a. 7

Referring now to the details of the film motion damper shown in Figs. 2to 5inclusive, the arm is fixedly attachedtoa shaft 38 through a hub 34,the shaft having mounted thereon a light metal plate 3! Attached to theplate I! in any suitable manner such as by glueor coupled by rougheningthe surface of plate 3!, is a soft felt pad 40. A cup-shaped housing 40encloses the plate -39 and felt II and also a stainless steel plate 4|pressed into the bottom of the cup.

This plate is'polished preferably by'rotary mo- 75 tion to a very highdegree on the side thereof contacting felt 40. The felt 4| and plate 4|have a motion relative to one another to provide the sliding frictioncharacteristic of the invention, the static friction therebetween beingless than the kinetic friction, although satisfactory op; eration isobtainable with materials in which these frictions are equal in, value.Other materials or constructions having similar characteristics may,therefore, be used.

To maintain a uniform pressure between the plate and felt 40, a'coilspring 43 is employed, one end of which abuts the end of shaft 38 andthe other end of, which is fitted into a notch of a lever arm 44 pivotedon a projection 45. The

lever arm 44 may be adjusted to'increase or decrease the compression ofspring 43 and consequently the pressure between plate 4| and felt 40, bya long screw 46 threaded through a back plate 4'! of the casing orhousing 48. This particular arrangement permits the adjustment to bemade from the front of the reproducer. As shown in Fig. 5, the steelplate 39 and felt 40 have V-type slots 49 provided therein to permitoscillation of the shaft. 38. The back plate 41 is attached to thecasing 48 by means of a plurality of screws 5| while the entire unit isfixed against rotation by attachment to the frame or housing 5 by screws3i through holes Si in the casing 48.

It will be seen in Fig. 1 that the film advance by the sprocket l4drives or rotates the spool 22 and the flywheel 21. In starting a.sudden ten- .sion is placed on the film 13 between the sprocket l4 andthe spool 22 which'pulls the arm 32 upward, decreases the loop andstores energy in the tensioning spring 35.

Referring now to Fig. 6 in which the counter:

force of friction F of the damper is plotted against the relativevelocities "V of the friction surfaces of the damper caused by filmspeed variations or surges, there is shown a pair of dotted lines B andBI" which illustrate the action of two usual types of sliding frictionresistance, a'pair of dot and dash lines A and Al" which illustrate theaction of two viscous types of dampers, and a solid line "1 illustratingthe action of an ideal damper of this invention. These curves may beconsidered as the force-velocity characteristics of difierent types ofdampers.

It will be observed from curve 'i" that the slope is initially steep sothat adequate damping is obtained at the low velocities which areencountered in the free period oscillation. For higher velocities theslope rapidly decreases so that rapid surges do not generate highcounterforces which accelerate the flywheel or cause slipping of thefilm on the drum or spool. Now, in curve A", which illustrates a viscoustype .damper adjusted to rapidly damp the free period oscillation, therewill be unduly high counterforces offered to high velocity surges whichwill cause appreciable acceleration of the flywheel or slippage of thefilm. While the latter objection is eliminated with curve Al", thedamping in this case would not be suflicient. v In the case of curves Band BI where the usual characteristics of sliding friction areillustrated, there are abrupt changes in counteriorce wherever thevelocity passes through zero. These changes set up transient surgeswhich are objectionable in film drive filters.

What is claimed is:

1. In a film drive system, the combination of a drive sprocket, astabilizing means adapted to be driven by a fllmadvanced by saidsprocket,

said film, having a loop therein between said drive sprocket and saidmeansrsaid loop varying in size in accordance with variations in speedof said film and means including a sliding friction damper located insaid loop and offering, av substantially constant counterforce to vsaidvariations in the size of said loop over a certain range of velocitiesof variations and proportional counterforces to variations in velocitiesoutside of said range.

2. A film drive system comprising a continuously driven sprocket, afiywheelroller, means for guiding the film between said roller and saidsprocket in the form of a loop tending to move said guiding means duringchanges in speed of said film, and means including a sliding frictiondamper movable by said guiding means for introducing a substantiallyconstant counterforce to changes in speed of said film within apredetermined range and proportional counterforces to changes in speedof said film below said range.

3. A film motion damper comprising a steel plate, felt materialpositioned in contact with said plate and adapted to be oscillated,means for adjusting the pressure between said felt and said plate, andmeans interconnecting a moving film and said felt for oscillating saidfelt, the friction between said felt and said plate constituting acounterforce to variations in speed of said film.

4. A film drive system comprising means for driving a motion picturefilm at a substantially constant speed, means adapted to be rotated by afilm, means between said driving means and said rotatable means forforming a loop in said film, means attached to said loop forming meansand adapted to be displaced by changes in speed of said film, and asliding friction damper in- 'cluding a metal, and soft pliable materialin contact therewith. for resisting the displacement of said loopforming means and preventing speed changes from affecting said rotatablemeans.

5. A film drive system comprising a drive sprocket for a motion picturefilm, means adapted to be driven by the pull of said film forstabilizing the motion thereof, and .a sliding friction damperinterposed between said sprocket and said stabilizing means for reactingto changes in motion of said film at a substantially constantcounterforce and negligible static friction..

6. A film drive system in accordance with I claim 5 in which saidsliding friction damper includes steel in contact with soft felt, saiddamper having a resilient restoring member.

7. A film drive system comprising a sprocket adapted to advance a filmat a substantially constant speed, a stabilizing device adapted to berotated by the pull of said film, said device having considerable mass,and means including a sliding friction damper intermediate said sprocketand said device and adapted to be displaced by speed variations of saidfilm, said means providing a substantially constant counterforce todisplacement for variations in speed of said film at differentamplitudesand frequencies within a certain range of amplitudes and frequencies.

8. A film drive in accordance with claim '7 in which said slidingfriction damper includes soft felt and steel adapted to be moved by filmspeed variations relatively to one another, the pressure therebetweenbeing controllable.

9. In a film drive system the combination of a tension roller adapted toengage a loop in the film and a sliding friction brake device operatedby movements of said roller, said device having a 7 lower staticfriction than kinetic friction;

10. A film drive system comprising means for continuously advancing aiilm,-means for stabilizing the movement of said film, and a slidingfriction damper in a loop of'said film and directly operative by changesin size of said loop for absorbing mm speed variations and oscillationsof variations within the time of said stabilizing means. i

12. A drive system 1 comprising a. source of power, a mass adapted to berotated bysaid power. resilient means adapted to store and reoneoscillation of lease energy during variations in speed of said source ofpower, and a sliding friction damper connected to said resilientmeans,the rate of absorption of energy by said damper being proportional tocertain velocities of movement of said resilient meansand constant tocertain other velocities of movement of said resilient means.

13. A drive system in accordance with claim 12 in which said slidingfriction damper comprises felt and steel in contact with one another. Iv

mow J. HABBROUCK, Jin

